The present invention relates generally to radar systems, and specifically to a waveform generator for a synthetic aperture radar (SAR) system which generates waveforms which may be: frequency modulated (FM), biphase modulated, or a combination of both modulations.
The tasks of generating waveforms which may be modulated with a combination of frequency modulation and biphase modulation is alleviated, to some extent, by the following U.S. patents, which are incorporated herein by reference:
U.S. Pat. No. 4,176,328 issued to Brown et al; PA1 U.S. Pat. No. 4,177,706 issued to Greenberger; PA1 U.S. Pat. No. 4,347,403 issued to Schwager et al; PA1 U.S. Pat. No. 4,438,503 issued to White et al; PA1 U.S. Pat. No. 4,454,486 issued to Hassun et al; and PA1 U.S. Pat. No. 4,519,027 issued to Vogelsberg.
Waveform generators are disclosed for a variety of uses in the references cited above. White et al discloses a waveform synthesizer for calibrating VHF omnidirectional radio (VOR) equipment by synthesis of a series of waveforms representative of different positions in azimuth. The patented system involves combining information from first and second memory areas and passing the information through a digital-to-analog converter. In Hassun et al the synthesizer provides high frequency synthesized waveforms for a user. It combines digital information in parallel and may accomplish frequency and phase modulations of the synthesized waveforms.
Biphase modulation of carrier signals is disclosed in the Brown reference cited above. The Brown reference has been incorporated since it describes in detail a biphase modulator.
While the references of Brown and White et al are exemplary in the art, a need still remains to produce waveforms which are combinations of frequency modulated carriers and biphase modulation. The present invention is intended to satisfy that need.